Silicon-carbon material, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a silicon-carbon material and a preparation method and application thereof. The silicon-carbon material comprises a core and a coating layer coated on at least part of the surface of the core; the core comprises a nano-silicon material; the coating layer comprises a flexible conductive polymer layer and a carbon layer existing between the core and the flexible conductive polymer layer; the flexible conductive polymer layer comprises a conductive polymer, and the conductive polymer has a conjugated structure; the conductive polymer comprises at least one of polyaniline, polypyrrole, polyacetylene, polythiophene, polyquinoline, polyfluorene, polybenzothiadiazole and poly-p-phenylene-vinylene; wherein the ratio of the mass of the conductive polymer to the total mass of the carbon layer and the core is (0.05-0.2):1. By constructing a shell layer structure with a "carbon layer-flexible coating layer" on the core, the silicon-carbon material with the core-shell structure can solve the problems of volume expansion, poor conductivity and unstable SEI layer of the silicon material in the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a silicon-carbon material, its preparation method, and its application. Background Technology

[0002] Silicon-based anode materials, with their theoretical specific capacity as high as 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite anodes, are considered core materials for next-generation lithium-ion batteries and are widely used in electric vehicles, energy storage systems, and consumer electronics. However, silicon materials react with lithium during charging and discharging to form Li₂... 4.4 The high volume expansion rate of silicon alloys (up to 300%) leads to structural collapse, loss of active materials, and decreased conductivity, severely hindering their commercial application. Furthermore, silicon itself has low conductivity (5 × 10⁻⁶). -4 The repeated generation and rupture of the solid electrolyte interphase (SEI) layer (S / cm) and the solid electrolyte interphase (SEI) layer further lead to a shortened battery cycle life and low initial charge-discharge efficiency (typically below 60%).

[0003] In existing technologies, modification schemes for silicon anode materials mainly focus on the following directions:

[0004] Carbon coating technology: This involves coating the surface of silicon particles with a layer of graphene, carbon nanotubes, or amorphous carbon to mitigate volume expansion and improve conductivity. However, the mechanical strength of a single carbon layer is insufficient to effectively suppress crack propagation within the silicon particles, resulting in unsatisfactory cycle stability.

[0005] Polymer buffer layer technology: Flexible polymer materials such as polyacrylonitrile (PAN) and polystyrene (PS) are used as buffer layers to absorb the expansion stress of silicon through their elastic deformation. However, these materials are prone to creep or degradation after long-term cycling, leading to the failure of the coating layer and the inability to maintain structural stability.

[0006] Composite coating technology: Some studies have attempted to combine carbon layers with polymer materials, but the existing schemes lack sufficient density, interfacial stability and synergistic effect of the coating layer, making it difficult to solve the multiple problems of volume expansion, poor conductivity and instability of the SEI layer at the same time.

[0007] Therefore, developing a silicon-carbon composite anode material that can effectively suppress volume expansion, improve conductivity, and stabilize the SEI layer is a key technological path to realize high-energy-density lithium-ion batteries. Summary of the Invention

[0008] In view of this, the present invention provides a silicon-carbon material, its preparation method and application. By constructing a shell structure with a "carbon layer-flexible coating layer" on the core, the silicon-carbon material with this core-shell structure can solve the problems of volume expansion, poor conductivity and unstable SEI layer of silicon materials in lithium-ion batteries.

[0009] In a first aspect, the present invention provides a silicon-carbon material comprising a core and a coating layer covering at least a portion of the surface of the core; the core comprising nano-silicon material; the coating layer comprising a flexible conductive polymer layer and a carbon layer present between the core and the flexible conductive polymer layer; the flexible conductive polymer layer comprising a conductive polymer having a conjugated structure; the conductive polymer comprising at least one of polyaniline, polypyrrole, polyacetylene, polythiophene, polyquinoline, polyfluorene, polybenzothiadiazole, and poly(p-phenylenevinylene).

[0010] The ratio of the mass of the conductive polymer to the total mass of the carbon layer and the core is (0.05-0.2):1.

[0011] As described above, the carbon layer of the silicon-carbon material comprises graphite and magnesium oxide particles.

[0012] As described above, in the silicon-carbon material, the carbon layer is doped with nitrogen.

[0013] As described above, the silicon-carbon material includes a first carbon layer formed by resin carbonization and a second carbon layer formed by pitch carbonization, wherein the first carbon layer is located between the core and the second carbon layer.

[0014] As described above, the first carbon layer of the silicon-carbon material comprises amorphous carbon and graphite; the second carbon layer comprises amorphous carbon and magnesium oxide particles.

[0015] As described above, the silicon-carbon material has a particle size D90 of 50 nm-150 nm.

[0016] Secondly, the present invention provides a method for preparing silicon-carbon material as described above, comprising the following steps: coating the nano-silicon material with a carbon source to form a carbon layer on at least a portion of the surface of the nano-silicon material to obtain a first intermediate; coating the first intermediate with a conductive polymer to form a flexible conductive polymer layer on the surface of the first intermediate to obtain the silicon-carbon material.

[0017] The method for preparing silicon-carbon materials as described above, wherein the process of coating the nano-silicon material with a carbon source includes: subjecting a first slurry containing the nano-silicon material and a first carbon source to a first drying treatment to obtain a first dried product; subjecting the first dried product to a first carbonization treatment to obtain a first intermediate; subjecting a first material containing the first intermediate and a second carbon source to a second carbonization treatment to obtain a second intermediate; and subjecting a second material containing the second intermediate and a conductive polymer to a reaction with an acidic solution, followed by a second drying treatment to obtain the silicon-carbon material.

[0018] In the method for preparing silicon-carbon materials as described above, the first carbon source includes resin and graphite.

[0019] In the method for preparing silicon-carbon materials as described above, the mass ratio of the nano-silicon material to the resin is 1:(0.1-0.3).

[0020] In the method for preparing silicon-carbon materials as described above, the mass ratio of the nano-silicon material to the graphite is (1-3):1.

[0021] In the method for preparing silicon-carbon materials as described above, the first slurry further includes a nitrogen-containing compound;

[0022] The method for preparing silicon-carbon materials as described above, wherein the nitrogen-containing compound includes at least one of melamine, urea, pyridine, pyrrole, ethylenediamine, trimethylamine, and aniline.

[0023] In the preparation method of silicon-carbon materials described above, the mass of the nitrogen-containing compound accounts for 1%-5% of the mass of the nano-silicon material.

[0024] As described above in the method for preparing silicon-carbon materials, the first slurry further includes a dispersant, which includes at least one of hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and polyvinylpyrrolidone.

[0025] As described above, in the method for preparing silicon-carbon materials, the first dried product is subjected to isostatic pressing and shaping treatment, and then subjected to the first carbonization treatment; wherein, the pressure of the isostatic pressing and shaping treatment is 8000 N-20000 N.

[0026] In the silicon-carbon material preparation method described above, the temperature of the first carbonization treatment is 600℃-800℃, and the time is 2 h-4 h.

[0027] As described above in the method for preparing silicon-carbon materials, the first material further includes a pre-magnesium agent, which includes at least one of magnesium hydroxide, dibutylmagnesium, and diethylmagnesium.

[0028] In the preparation method of silicon-carbon material described above, the mass of the pre-magnesium agent accounts for 2%-6% of the mass of the first intermediate.

[0029] In the method for preparing silicon-carbon materials as described above, the second carbon source includes pitch, and the mass ratio of the pitch to the first intermediate is (0.2-0.4):1.

[0030] In the silicon-carbon material preparation method described above, the temperature of the second carbonization treatment is 1200℃-1400℃, and the time is 3 h-6 h.

[0031] In the method for preparing silicon-carbon materials as described above, the second material further includes an oxidant, which includes hydrogen peroxide and / or ammonium persulfate.

[0032] In the method for preparing silicon-carbon materials as described above, the acidic solution includes a dodecylbenzenesulfonic acid solution and / or a hydrochloric acid solution.

[0033] In the preparation method of silicon-carbon material described above, the reaction time between the second material and the acidic solution is 2 h to 10 h.

[0034] Thirdly, the present invention provides a negative electrode sheet, comprising silicon-carbon material prepared by the method described above.

[0035] Fourthly, the present invention provides a lithium-ion battery comprising the negative electrode sheet described above.

[0036] The present invention, employing the above-described solution, has at least the following beneficial effects:

[0037] In this application, by constructing a shell layer with a "carbon layer-flexible coating layer" on the core, the silicon-carbon material with this core-shell structure can absorb silicon expansion stress through the carbon layer, and the flexible coating layer can buffer volume changes through elastic deformation, forming a stress buffering synergistic effect. This avoids particle pulverization, structural collapse, and poor cycle stability caused by volume expansion in lithium-ion batteries, thereby improving the conductivity of silicon-carbon materials and the stability of the SEI layer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0039] To address the volume expansion issue of silicon anode materials in lithium-ion batteries, the inventors studied the coating structure of silicon anode materials. They found that existing technologies use a single carbon layer to coat silicon particles, but the mechanical strength of a single carbon layer is insufficient to effectively suppress crack propagation within the silicon particles, resulting in unsatisfactory cycle stability. Other technologies use polymer materials to coat silicon particles, but these materials are prone to creep or degradation after long-term cycling, leading to coating layer failure and an inability to maintain structural stability. Still other technologies combine a single carbon layer with polymer materials to coat silicon particles, but this combined coating lacks sufficient density, interfacial stability, and synergistic effects, making it difficult to simultaneously solve the multiple problems of volume expansion, poor conductivity, and SEI layer instability.

[0040] The inventors improved the coating of silicon nanoparticles, increasing the density and integrity of the coating and working synergistically to solve the problems of silicon volume expansion and low initial charge-discharge efficiency, and to improve the cycle life and stability of the battery.

[0041] In view of this, embodiments of this application propose a silicon-carbon material comprising a core and a coating layer covering at least a portion of the surface of the core; the core comprises nano-silicon material; the coating layer comprises a flexible conductive polymer layer and a carbon layer existing between the core and the flexible conductive polymer layer; the flexible conductive polymer layer comprises a conductive polymer having a conjugated structure; the conductive polymer comprises at least one of polyaniline, polypyrrole, polyacetylene, polythiophene, polyquinoline, polyfluorene, polybenzothiadiazole, and poly(p-phenylenevinylene); wherein the ratio of the mass of the conductive polymer to the total mass of the carbon layer and the core is (0.05-0.2):1.

[0042] According to the inventors' research, by coating a carbon layer and a flexible conductive polymer layer onto nano-silicon materials, a shell structure with a "carbon layer-flexible coating layer" is formed. The carbon layer can absorb the silicon expansion stress, and the flexible coating layer can buffer the volume change through elastic deformation, forming a stress buffering synergistic effect, which in turn creates a synergistic effect of stress buffering and enhanced conductivity. This avoids particle pulverization, structural collapse, and poor cycle stability caused by volume expansion in lithium-ion batteries, thereby improving the conductivity of silicon-carbon materials and the stability of the SEI layer.

[0043] In one specific embodiment, the aforementioned flexible conductive polymer layer comprises a conductive polymer having a conjugated structure. The conjugated structure contains a delocalized π-electron system, allowing electrons to move freely along the conjugated chains, endowing the polymer with good electronic conductivity. This facilitates the construction of continuous electron transport channels, compensating for the potential defects of the carbon layer conductive network. By employing a conductive polymer with a conjugated structure as the flexible layer, not only can electron transport efficiency be improved, but the expansion stress of silicon can also be further absorbed, achieving flexible buffering.

[0044] In one specific embodiment, the conductive polymer includes at least one selected from polyaniline, polypyrrole, polyacetylene, polythiophene, polyquinoline, polyfluorene, polybenzothiadiazole, and poly(p-phenylenevinylene). In this embodiment, the specific selection of the conductive polymer is not limited. All of the above conductive polymers contain a conjugated structure, which not only improves electron transport efficiency but also further absorbs the expansion stress of silicon, achieving flexible buffering.

[0045] In one specific embodiment, the mass ratio of the conductive polymer to the total mass of the carbon layer and the core can be (0.05-0.2):1. Exemplarily, the mass ratio can be 0.05:1, 0.1:1, 0.13:1, 0.17:1, 0.2:1, or any ratio between two of these. A mass ratio not less than 0.05 helps to form a continuous coating layer of a certain thickness, thereby providing sufficient elastic buffering and effective isolation protection; a mass ratio not greater than 0.2 helps to avoid a significant decrease in the overall energy density (especially capacity) of the material due to an excessively thick inactive coating layer, and prevents an increase in ion transport resistance that may be caused by an excessively thick coating layer. By controlling the above parameters, the conductive polymer can form a continuous conductive network, improving electrical performance, enhancing flexibility, and preventing crack propagation.

[0046] In one specific embodiment, the carbon layer comprises graphite and magnesium oxide particles. The layered crystal structure of graphite provides a good electronic conduction path, reducing the internal resistance of the electrode; after subsequent acid washing and removal, the magnesium oxide particles leave voids in the carbon layer, which provide space for the volume expansion of silicon during charging and discharging, thus alleviating the stress of the overall structure.

[0047] In one specific embodiment, the carbon layer is doped with nitrogen. By doping the carbon layer with nitrogen, the conductivity of the carbon layer can be further improved, and the silicon-carbon interface bonding force can be enhanced through CN bonds, thereby suppressing crack propagation.

[0048] In one specific embodiment, the carbon layer comprises a first carbon layer formed by resin carbonization and a second carbon layer formed by pitch carbonization, wherein the first carbon layer is located between the core and the second carbon layer. The first carbon layer comprises amorphous carbon and graphite; the second carbon layer comprises amorphous carbon and magnesium oxide particles.

[0049] Specifically, the amorphous carbon in the first carbon layer is formed by carbonizing the resin carbon layer. This first carbon layer can effectively coat the core, making the silicon less prone to cracking during charging and discharging, maintaining good conductivity and ion transport efficiency, and suppressing the volume expansion of silicon particles, thereby significantly improving the battery's fast charging performance and cycle life.

[0050] Specifically, the amorphous carbon in the first carbon layer is formed by the carbonization of the pitch carbon layer. During the carbonization process, the pitch carbon layer forms amorphous carbon, which coats the first intermediate, absorbing the expansion stress of the silicon material and enhancing the stability of the carbon layer structure. Meanwhile, the magnesium oxide particles, dispersed in the formed second carbon layer, form a stable inorganic SEI layer, compensating for irreversible capacity loss. Through the coating of multiple carbon layers, direct contact between the silicon material and the electrolyte can be blocked, suppressing side reactions.

[0051] Specifically, the average particle size of the aforementioned nano-silicon material is less than or equal to 150 nm.

[0052] In one specific embodiment, the particle size D90 of the aforementioned nano-silicon material can be 50 nm to 150 nm. For example, the particle size D90 of the nano-silicon material can be 50 nm, 80 nm, 100 nm, 130 nm, 150 nm, or any two of these ranges. A particle size D90 of not less than 50 nm helps to reduce the specific surface area of ​​the material, decrease the amount of SEI film formed, and simultaneously helps to suppress the aggregation of silicon particles, maintaining the microstructural stability of the material. A particle size D90 of not more than 150 nm helps to shorten the lithium-ion diffusion path, improve the rate performance of the material, and simultaneously disperse volume expansion stress, reduce the risk of silicon particle breakage and interface peeling, and improve cycle stability.

[0053] This application also provides a method for preparing silicon-carbon material, comprising the following steps: coating nano-silicon material with a carbon source to form a carbon layer on at least a portion of the surface of the nano-silicon material to obtain a first intermediate; coating the first intermediate with a conductive polymer to form a flexible conductive polymer layer on the surface of the first intermediate to obtain the silicon-carbon material.

[0054] According to the inventor's research, by using the above-mentioned technical means, a carbon layer-flexible coating shell structure is constructed by first coating nano-silicon with a carbon source and then using a conductive polymer for flexible coating. The carbon layer can absorb the expansion stress of silicon, and the flexible coating layer can buffer the volume change through elastic deformation, forming a stress buffering synergistic effect. This avoids particle pulverization, structural collapse and poor cycle stability caused by volume expansion in lithium-ion batteries, thereby improving the conductivity of silicon-carbon materials and the stability of the SEI layer.

[0055] In one specific embodiment, the process of coating nano-silicon materials with a carbon source includes: subjecting a first slurry containing nano-silicon materials and a first carbon source to a first drying treatment to obtain a first dried product; subjecting the first dried product to a first carbonization treatment to obtain a first intermediate; subjecting a first material containing the first intermediate and a second carbon source to a second carbonization treatment to obtain a second intermediate; and reacting the second material containing the second intermediate and a conductive polymer with an acidic solution, followed by a second drying treatment to obtain a silicon-carbon material. By subjecting the first carbon source and nano-silicon materials to a first drying treatment and the first carbonization treatment, the first carbon source can be formed into an amorphous carbon layer, improving conductivity and suppressing silicon particle volume expansion; and by subjecting the second carbon source and the first intermediate to a second carbonization treatment, the second carbon source can be formed into rigid amorphous carbon, which is then coated onto the first intermediate, thereby forming a rigid carbon layer. The conductive polymer is then coated onto the second intermediate to form a flexible coating layer, thereby giving the prepared silicon-carbon material a rigid-flexible multilayer coating, which can avoid the problems of particle pulverization, structural collapse, and poor cycle stability caused by volume expansion in lithium-ion batteries.

[0056] In one specific embodiment, the first carbon source includes resin and graphite. By carbonizing the resin to form a first carbon layer, an amorphous carbon layer can be formed on the surface of the nano-silicon material, suppressing the volume expansion of the nano-silicon material during charging and discharging; while graphite can serve as a conductive framework, shortening the electron transport path and improving conductivity.

[0057] Specifically, the resins mentioned above include at least one of phenolic resin, epoxy resin, silicone resin, polyurethane resin, and polyacrylic resin. In this embodiment, the choice of resin type is not limited.

[0058] Specifically, the graphite mentioned above includes natural flake graphite and artificial graphite; it can effectively suppress the volume expansion of silicon particles.

[0059] In one specific embodiment, the mass ratio of the aforementioned silicon nanoparticles to the aforementioned resin can be 1:(0.1-0.3); exemplaryly, the mass ratio can be 1:0.1, 1:0.5, 1:0.2, 1:0.25, 1:0.3, or any ratio range between the above. A resin ratio of not less than 0.1 helps to form a continuous and sufficiently thick initial amorphous carbon coating layer, providing effective initial protection and buffering for the silicon core; a resin ratio of not more than 0.3 helps to prevent an excessively thick amorphous carbon layer from causing a decrease in the overall conductivity and capacity contribution of the material. By controlling the above parameters, the resin can be uniformly coated on the silicon nanoparticles, and after carbonization, the first carbonized layer formed can suppress the volume expansion of the silicon nanoparticles during charging and discharging.

[0060] In one specific embodiment, the mass ratio of the aforementioned silicon nanoparticles to the aforementioned graphite can be (1-3):1; exemplaryly, the mass ratio can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any ratio range between two of the above. A mass ratio not lower than 1:1 helps ensure sufficient graphite component in the carbon layer to provide excellent conductivity; a mass ratio not higher than 1:3 helps control the content of inactive graphite in the material, avoiding excessive negative impact on the overall specific capacity. By controlling the amount of graphite added, it is beneficial to improve the overall conductivity of the material and adjust the specific capacity of the composite material.

[0061] In one specific embodiment, the first slurry further includes a nitrogen-containing compound; the nitrogen-containing compound includes at least one selected from melamine, urea, pyridine, pyrrole, ethylenediamine, trimethylamine, and aniline. In this embodiment, the specific type of nitrogen-containing compound is not limited. By adding a nitrogen-containing compound, stable CN chemical bonds can be formed, optimizing the coating stability and conductivity of the first carbon layer.

[0062] In one specific embodiment, the mass of the nitrogen-containing compound accounts for 1%-5% of the mass of the nano-silicon material, and exemplaryly, it can be in the range of any two of 1%, 2%, 3%, 4%, 5%, or more. A mass of not less than 1% of the nitrogen-containing compound helps to introduce a sufficient number of nitrogen-active sites into the carbon layer, improving its electrochemical performance; a mass of not more than 5% of the nitrogen-containing compound helps to avoid the decomposition of excessive nitrogen-containing compounds, generating too much gas or residual impurities, which could affect the density and structural stability of the carbon layer.

[0063] In one specific embodiment, the first slurry further includes a dispersant, which includes at least one selected from hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and polyvinylpyrrolidone; in this embodiment, the specific type of dispersant is not limited. Adding a dispersant helps to uniformly disperse solid particles such as nano-silicon and graphite in the slurry, preventing agglomeration and laying the foundation for the subsequent formation of a uniform and continuous carbon coating layer. This is a key process step in improving the uniformity of material structure and the consistency of performance.

[0064] In one specific embodiment, the first dried product is subjected to isostatic pressing and then to a first carbonization treatment; wherein the pressure of the isostatic pressing treatment is 8000 N-20000 N; exemplaryly, the pressure can be 8000 N, 10000 N, 14000 N, 15000 N, 20000 N, or any range between the above. By subjecting the first dried product to isostatic pressing and controlling the pressure of isostatic pressing, the density uniformity of the first dried product can be improved, internal defects can be reduced, and the structural stability of the first dried product can be enhanced, preventing cracking during the first carbonization process.

[0065] In one possible implementation, during the isostatic pressing process, dynamic pressure control is employed, gradually increasing the pressure from 8000 to 20000 N. For example, isostatic pressing is performed first at 8000 N, then at 15000 N, and finally at 20000 N, thereby forming a dense-loose alternating layered structure. This allows for the formation of a dense-loose alternating first carbon layer during the first carbonization, which is beneficial for increasing the bonding force between graphite and nano-silicon and further buffering the volume expansion of the nano-silicon material during charging and discharging.

[0066] In one specific embodiment, the temperature of the first carbonization treatment is 600-800°C, and the time is 2-4 hours. Exemplarily, the temperature can be any range between 600°C, 650°C, 700°C, 750°C, 800°C, or any two of these; the time can be any range between 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these. By controlling the temperature of the first carbonization treatment, the resin can form a dense structure, forming a rigid first carbon layer, which can suppress the volume expansion of the nano-silicon material during charging and discharging.

[0067] In one specific embodiment, the first material further includes a pre-magnesium agent, which includes at least one of magnesium hydroxide, dibutylmagnesium, and diethylmagnesium; in this embodiment, the specific selection of the pre-magnesium agent is not limited. By adding the pre-magnesium agent, magnesium oxide particles can be introduced into the second intermediate, so that the second intermediate pre-forms an inorganic SEI layer, which can compensate for irreversible capacity during the charging and discharging process of the silicon material.

[0068] In one specific embodiment, the pre-magnesium agent accounts for 2%-6% of the mass of the first intermediate; exemplary, it is within any two of 2%, 3%, 4%, 5%, 6%, or more. A pre-magnesium agent mass of not less than 2% helps to generate a sufficient amount of magnesium oxide to provide reinforcement and support; a pre-magnesium agent mass of not more than 6% helps to avoid excessive magnesium oxide aggregation, which could affect the continuity and conductivity of the carbon layer.

[0069] In one specific embodiment, the second carbon source includes asphalt. The asphalt includes at least one of natural asphalt, petroleum asphalt, and coal tar pitch; in this embodiment, the specific choice of asphalt is not limited. By selecting asphalt as the second carbon source, the rigid amorphous carbon layer after carbonization further enhances the structural stability of the carbon layer.

[0070] In one possible implementation, the mass ratio of the asphalt to the first intermediate is (0.2-0.4):1. Exemplarily, the mass ratio can be 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, or any ratio between two of these. An asphalt ratio of not less than 0.2 helps form a sufficiently thick second carbon layer, providing effective mechanical protection and a conductive network; an asphalt ratio of not more than 0.4 helps prevent an excessively thick carbon layer from increasing the inactive mass of the material and potentially hindering lithium-ion transport due to excessive coating thickness. By controlling the amount of asphalt added, the first intermediate can be uniformly coated, and the coating thickness of the second carbon layer can be controlled.

[0071] In one specific embodiment, the temperature of the second carbonization treatment is 1200℃-1400℃, and the time is 4h-6h. Exemplarily, the temperature can be any ratio between 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, or any two of these. The time can be any ratio between 4h, 4.5h, 5h, 5.5h, 6h, or any two of these. By controlling the carbonization temperature of the asphalt, the pore structure after asphalt carbonization can be optimized, and a gradient change can be formed with the pore structure formed after resin carbonization. This reduces the interfacial stress between the first carbon layer and the second carbon layer, improves the stability of the carbon layer structure, and enhances the absorption of expansion stress during the charging and discharging process of the silicon material, thereby contributing to improved cycle stability.

[0072] In one possible implementation, the preparation of the second intermediate further includes: dissolving asphalt in a solvent, adding a soft template agent, and dispersing it into a homogeneous solution; then self-assembling it at 40℃-80℃ for 2 h-8 h to obtain an assembly liquid; then drying the assembly liquid and carbonizing it to obtain the second intermediate.

[0073] By adding a soft template agent, a mesoporous structure can be introduced into the second carbon layer after asphalt carbonization, which can enrich the pore structure of the second carbon layer. On the one hand, the introduced mesoporous structure can provide a buffer space for the expansion of silicon material and reduce the volume expansion rate during cycling. On the other hand, the introduced mesoporous structure increases the contact area between the electrolyte and the silicon material and improves the uniformity of the SEI layer.

[0074] Specifically, the solvent mentioned above includes at least one of chloroform and toluene. In this embodiment, the specific choice of solvent is not limited.

[0075] Specifically, the aforementioned soft template agent includes at least one of block copolymers and surfactants. For example, the block copolymer includes at least one of block copolymer F127 and block copolymer P123. The surfactant includes hexadecyltrimethylammonium bromide.

[0076] Specifically, in the above carbonization process, the heating rate is 1℃ / min-3℃ / min. For example, the heating rate can be 1℃ / min, 2℃ / min, 3℃ / min, or any range between these two. By controlling the heating rate, the structural collapse caused by excessively rapid decomposition of the soft template agent is prevented. During the heating process, the solvent and gases released from the decomposition of the soft template agent are volatilized.

[0077] Specifically, a pre-magnesium agent can be added after the soft template agent is added to form a self-assembly liquid, in order to reduce potential interference with the self-assembly liquid.

[0078] In one specific embodiment, the second material further includes an oxidant, which may include hydrogen peroxide and / or ammonium persulfate. The addition of the oxidant initiates the reaction of the conductive polymer, facilitating subsequent reactions.

[0079] In one specific embodiment, the acidic solution comprises a dodecylbenzenesulfonic acid solution and / or a hydrochloric acid solution; the pH of the dodecylbenzenesulfonic acid solution can be 4-6, preferably 5.

[0080] In one specific embodiment, the reaction time between the second material and the acidic solution is 2 h to 10 h. Exemplarily, the reaction time can be 2 h, 4 h, 6 h, 8 h, 10 h, or any combination thereof. Under acidic conditions, the in-situ polymerization of the conductive polymer is initiated by an oxidant, forming a flexible coating layer whose conjugated structure can effectively conduct electrons and shorten the lithium-ion diffusion path.

[0081] In a specific implementation, nano-silicon materials, nitrogen-containing compounds, a first carbon source, and a dispersant are mixed to form a first slurry; the first slurry is subjected to a first drying treatment to obtain a first dried product; the first dried product is subjected to a first carbonization treatment to obtain a first intermediate; the first intermediate is mixed with a second carbon source and a pre-magnesium agent, dried, and then subjected to a second carbonization treatment to obtain a second intermediate; the second intermediate is dispersed with an oxidant and a conductive polymer in an acidic solution, washed, and then subjected to a second drying treatment to obtain the silicon-carbon material.

[0082] This application also provides a negative electrode sheet, comprising the silicon-carbon material as described above, or the silicon-carbon material prepared according to the silicon-carbon material preparation method described above.

[0083] Specifically, the negative electrode sheet of the present invention includes a negative current collector and a negative active layer formed of a negative active material disposed on the surface of the negative current collector.

[0084] In the specific preparation of the negative electrode, the negative electrode active material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained.

[0085] In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0086] The negative electrode current collector layer can be made of at least one of copper foil, nickel foam, and copper foam; the conductive agent can be made of at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; and the binder can be made of at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0087] This application also provides a lithium-ion battery, including the negative electrode sheet described above.

[0088] It is conceivable that, in addition to the aforementioned negative electrode, the lithium-ion battery of the present invention also includes a positive electrode, an electrolyte, and a separator.

[0089] In addition, the above-mentioned positive electrode sheet includes a positive current collector and a positive coating on at least one side surface of the positive current collector. Specifically, the positive coating can be provided on one side surface of the positive current collector, or the positive coating can be provided on the opposite two sides of the positive current collector in the thickness direction (i.e., the positive and negative surfaces of the positive current collector).

[0090] Specifically, the positive electrode coating includes materials such as positive electrode active materials, conductive agents, and binders.

[0091] This invention does not strictly limit the positive electrode active material in the positive electrode sheet; it can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, lithium-rich manganese-based materials, etc.

[0092] In addition, the conductive agent in the positive electrode coating may include one or more of conductive carbon black (Super. P), conductive graphite, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder in the positive electrode coating may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0093] In this embodiment of the invention, conventional positive current collectors in the art can be used, for example, the positive current collector includes aluminum foil.

[0094] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive active material, conductive agent, binder, and other components used to form the positive active material layer can be dispersed in a positive electrode solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0095] This invention does not strictly limit the choice of electrolyte, and may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0096] This invention does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0097] In this embodiment of the invention, liquid batteries can be prepared using conventional methods in the art. The preparation process may include: during the preparation of a lithium-ion battery, winding or stacking a positive electrode, a separator, and a negative electrode to obtain a bare cell, and then encapsulating the bare cell in a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85°C, electrolyte is injected into the dried battery. After the battery undergoes resting, formation, and secondary sealing, the preparation of the lithium-ion battery is completed.

[0098] Unless otherwise specified, the coating, drying, rolling and other processes involved in this application are all conventional operations in the field, and the equipment used can be conventional equipment in the field, without any special restrictions.

[0099] The silicon-carbon material of this application will be described in detail below through specific embodiments.

[0100] Example 1

[0101] Preparation of silicon-carbon materials:

[0102] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm and 35g of melamine in 200mL of ethanol, and then mill them to obtain nano-silicon slurry with a particle size of 130 nm.

[0103] Step 2: Mix 200mL of nano-silica slurry, 30mL of phenolic resin, 42g of natural flake graphite, and 3.6g of hydroxypropyl methylcellulose (HPMC) to form the first slurry.

[0104] Step 3: After spray drying, the slurry is used to obtain the first dried product; the first dried product is isostatically shaped under a pressure of 10000 N, and then carbonized at a temperature of 800℃ for 4 hours to obtain the first intermediate.

[0105] Step 4: Mix 100g of the first intermediate with 30g of natural asphalt and magnesium hydroxide, and dynamically dry under vacuum stirring at 100℃. After dynamic drying, carbonize at 1200℃ for 6 hours to obtain the second intermediate coated with asphalt carbon layer.

[0106] Step 5: Disperse 100g of the second intermediate with 10g of polyaniline and 2.1g of ammonium persulfate in 300mL of hydrochloric acid, react for 5 h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0107] Example 2

[0108] Preparation of silicon-carbon materials:

[0109] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm and 35g of melamine in 200mL of ethanol, and then mill them to obtain nano-silicon slurry with a particle size of 80 nm.

[0110] Step 2: Mix 200mL of nano-silica slurry, 20mL of phenolic resin, 68g of natural flake graphite, and 4.7g of hydroxypropyl methylcellulose (HPMC) to form a homogeneous slurry.

[0111] Step 3: After spray drying, the slurry is isostatically shaped under a pressure of 15000 N, and then carbonized at a temperature of 900℃ for 3 hours to obtain the first intermediate.

[0112] Step 4: Mix 100g of the first intermediate with 20g of natural asphalt and magnesium hydroxide, and dynamically dry under vacuum stirring at 100℃. After dynamic drying, carbonize at 1300℃ for 5 hours to obtain the second intermediate coated with asphalt carbon layer.

[0113] Step 5: Disperse 100g of the second intermediate with 5g of polyaniline and 0.6g of ammonium persulfate in 300mL of hydrochloric acid, react for 2h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0114] Example 3

[0115] Preparation of silicon-carbon materials:

[0116] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm and 35g of melamine in 200mL of ethanol, and then mill them to obtain nano-silicon slurry with a particle size of 80 nm.

[0117] Step 2: Mix 200mL of nano-silica slurry, 10mL of phenolic resin, 33g of natural flake graphite, and 2.2g of hydroxypropyl methylcellulose (HPMC) to form a homogeneous slurry.

[0118] Step 3: After spray drying, the slurry is isostatically shaped under a pressure of 20,000 N, and then carbonized at a temperature of 1000℃ for 2 hours to obtain the first intermediate.

[0119] Step 4: Mix 100g of the first intermediate with 40g of natural asphalt and magnesium hydroxide, and dynamically dry under vacuum stirring at 100℃. After dynamic drying, carbonize at 1400℃ for 4 hours to obtain the second intermediate coated with asphalt carbon layer.

[0120] Step 5: Disperse 100g of the second intermediate with 20g of polyaniline and 3.4g of ammonium persulfate in 300mL of hydrochloric acid, react for 10 h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0121] Example 4

[0122] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0123] In step one, urea is used instead of melamine, and the particle size of the nano-silicon is 50 nm.

[0124] Example 5

[0125] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0126] In step two, epoxy resin is used instead of phenolic resin, and the amount of epoxy resin used is 25 mL.

[0127] Example 6

[0128] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0129] In step two, silicone resin is used instead of phenolic resin, and the amount of silicone resin used is 28 mL.

[0130] Example 7

[0131] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0132] In step two, polypropylene resin is used instead of phenolic resin, and the amount of polypropylene resin used is 30 mL.

[0133] Example 8

[0134] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 2, except that:

[0135] In step two, hydroxyethyl cellulose is used instead of hydroxypropyl methyl cellulose, and the amount of hydroxyethyl cellulose used is 4.2g.

[0136] Example 9

[0137] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0138] In step three, the slurry is dried using a drum drying method. First, it is isostatically pressed for 3 minutes under a pressure of 8000N, and then isostatically pressed for 5 minutes under a pressure of 10000N.

[0139] Example 10

[0140] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 3, except that:

[0141] In step four, petroleum asphalt is used to replace natural asphalt, and dibutylmagnesium is used to replace magnesium hydroxide.

[0142] Example 11

[0143] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 3, except that:

[0144] In step four, 40g of natural asphalt is dissolved in 150mL of toluene, and then 10mL of hexadecyltrimethylammonium bromide and magnesium hydroxide are added and mixed. The mixture is stirred and dispersed into a homogeneous solution. The solution is then self-assembled at 60℃ for 6 hours to obtain the assembly solution. After the assembly solution is dynamically dried, it is heated to 1400℃ at a heating rate of 2℃ / min and then carbonized for 4 hours to obtain the second intermediate coated with asphalt carbon layer.

[0145] Example 12

[0146] In this embodiment, the preparation method of silicon-carbon material is the same as in Example 1, except that:

[0147] In step five, polypyrrole is used instead of polyaniline.

[0148] Comparative Example 1

[0149] In this comparative example, no nitrogen-containing compounds were added, based on Example 1, as follows:

[0150] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm in 200mL of ethanol, and then mill it to obtain nano-silicon slurry with a particle size of 130 nm.

[0151] Step 2: Mix 200mL of nano-silica slurry, 30mL of phenolic resin, 42g of natural flake graphite, and 3.6g of hydroxypropyl methylcellulose (HPMC) to form a homogeneous slurry.

[0152] Step 3: After spray drying, the slurry is isostatically shaped under a pressure of 10,000 N, and then carbonized at a temperature of 800℃ for 4 hours to obtain the first intermediate.

[0153] Step 4: Mix 100g of the first intermediate with 30g of natural asphalt and magnesium hydroxide, and dynamically dry under vacuum stirring at 100℃. After dynamic drying, carbonize at 1200℃ for 6 hours to obtain the second intermediate coated with asphalt carbon layer.

[0154] Step 5: Disperse 100g of the second intermediate with 10g of polyaniline and 2.1g of ammonium persulfate in 300mL of hydrochloric acid, react for 5 h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0155] Comparative Example 2

[0156] In this comparative example, no pre-magnesium agent was added, based on Example 1, as follows:

[0157] Preparation of silicon-carbon materials:

[0158] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm and 35g of melamine in 200mL of ethanol, and then mill them to obtain nano-silicon slurry with a particle size of 130 nm.

[0159] Step 2: Mix 200mL of nano-silica slurry, 30mL of phenolic resin, 42g of natural flake graphite, and 3.6g of hydroxypropyl methylcellulose (HPMC) to form a homogeneous slurry.

[0160] Step 3: After spray drying, the slurry is isostatically shaped under a pressure of 10,000 N, and then carbonized at a temperature of 800℃ for 4 hours to obtain the first intermediate.

[0161] Step 4: Mix 100g of the first intermediate with 30g of natural asphalt and dynamically dry it under vacuum stirring at 100℃. After dynamic drying, carbonize it at 1200℃ for 6 hours to obtain the second intermediate coated with asphalt carbon layer.

[0162] Step 5: Disperse 100g of the second intermediate with 10g of polyaniline and 2.1g of ammonium persulfate in 300mL of hydrochloric acid, react for 5 h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0163] Comparative Example 3

[0164] In this comparative example, based on Example 1, asphalt and pre-magnesium agents are not used, as follows:

[0165] Preparation of silicon-carbon materials:

[0166] Step 1: Disperse 100g of silicon powder with a particle size of 1-3μm and 35g of melamine in 200mL of ethanol, and then mill them to obtain nano-silicon slurry with a particle size of 130 nm.

[0167] Step 2: Mix 200mL of nano-silica slurry, 30mL of phenolic resin, 42g of natural flake graphite, and 3.6g of hydroxypropyl methylcellulose (HPMC) to form a homogeneous slurry.

[0168] Step 3: After spray drying, the slurry is isostatically shaped under a pressure of 10,000 N, and then carbonized at a temperature of 800℃ for 4 hours to obtain the first intermediate.

[0169] Step 4: Disperse 100g of the first intermediate, 10g of polyaniline, and 2.1g of ammonium persulfate in 300mL of hydrochloric acid, react for 5 h, wash three times with deionized water, and vacuum dry at 80℃ to obtain silicon-carbon material.

[0170] Test example:

[0171] 1. Preparation of half-cells

[0172] After the silicon-carbon materials used in all the examples and comparative examples were fabricated as negative electrode sheets, they were assembled with lithium metal sheets, electrolytes, and separators according to the following method to obtain a lithium-ion battery. The method includes:

[0173] 1) The silicon carbide material, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black from the examples and comparative examples were mixed in a weight ratio of 93%:2%:2%:3%. The mixture was dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. The slurry was coated onto a copper current collector, followed by rolling and drying to obtain a negative electrode sheet.

[0174] 2) Assemble lithium metal sheets, negative electrode sheets, and separators into a lithium-ion battery, and inject a non-aqueous electrolyte. The electrolyte is prepared by mixing ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, add 5% fluoroethylene carbonate (FEC) and 13% lithium hexafluorophosphate (LiPF6) by mass, along with the additive vinylene carbonate (VC), with the additive content accounting for 2% of the total electrolyte content.

[0175] 2. Cyclic Performance Testing: The batteries prepared above were subjected to cycle performance testing at 25°C room temperature. The testing procedure was as follows: first, constant current discharge at 0.2C to 0.005V, then rest for 5 minutes, then constant current discharge at 0.1C to 0.005V, then rest for 5 minutes, then constant current discharge at 0.01C to 0.005V; finally, constant current charging at 0.2C to 2.5V, and this cycle test was repeated. The capacity retention rate Q and thickness change rate after cycling were recorded.

[0176] Capacity retention rate Q = Q 500 / Q1×100%

[0177] Thickness change rate (%) = (D1 - D0) / D0 × 100%.

[0178] 3. Charge-discharge curves and initial coulombic efficiency

[0179] After each battery was left to stand at 25°C for 12 hours, its first charge-discharge capacity was tested. The test conditions were as follows: first, constant current discharge at 0.2C to 0.005V, then rest for 5 minutes, then constant current discharge at 0.1C to 0.005V, then rest for 5 minutes, then constant current discharge at 0.01C to 0.005V; finally, constant current charging at 0.2C to 2.5V. The first charge capacity C0 and the first discharge capacity D0 were recorded, and the first coulombic efficiency was calculated according to D0 / C0.

[0180] 4. Expansion rate test: Use a constant current charge and discharge program (e.g., charge to 0.005V at 0.1C, discharge to 0.005V at 0.05C / 0.02C, repeat multiple times).

[0181] Real-time thickness monitoring: Using an in-situ expansion analyzer (such as SWE2110) or displacement sensor, record the dynamic changes in electrode thickness during charging and discharging. Record the thickness in the fully charged state as T. max The initial thickness is T0. The expansion rate is calculated using the following formula:

[0182]

[0183] The test results of Examples 1-12 and Comparative Examples 1-3 are shown in Table 1:

[0184] Table 1

[0185]

[0186] As shown in Table 1, compared with Comparative Examples 1-3, the silicon-carbon material provided by this invention has comprehensive performance advantages. Examples 1-12 all exhibit excellent performance in terms of cycle performance, initial coulombic efficiency, and expansion suppression: the batteries of Examples 1-12 generally have a capacity retention rate of over 94% after 30 cycles, an initial coulombic efficiency of over 87.6%, and an expansion rate controlled below 50.5%, with a minimum of 34.8%. This result is attributed to the gradient coating and structural optimization strategy adopted in this invention. Nano-silicon is obtained through nitrogen-containing compound-assisted milling and a nitrogen source is introduced. A primary carbon skeleton is constructed with carbon sources such as phenolic resin and graphite. The structural density is enhanced by isostatic pressing. A dense and buffering coating layer is formed at high temperature using a pitch carbon layer and a pre-magnesium agent. The interface is further stabilized by treatment with conductive polymers such as polyaniline.

[0187] In summary, this invention effectively suppresses the volume effect of silicon and improves the mechanical stability and electrochemical reversibility of the electrode through the synergistic design of "nanosilicon + carbon skeleton + pitch carbon layer + interface modification", achieving a balanced optimization of high initial efficiency, long cycle life and low expansion.

[0188] It should be noted that: for experimental steps or conditions not specified in the examples, the procedures and conditions described in conventional experimental procedures in the literature of this art can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon material, characterized in that, The silicon-carbon material includes a core and a coating layer covering at least a portion of the surface of the core; the core includes nano-silicon material. The coating layer includes a flexible conductive polymer layer and a carbon layer existing between the core and the flexible conductive polymer layer; The carbon layer comprises graphite and magnesium oxide particles, and is doped with nitrogen. The carbon layer comprises a first carbon layer and a second carbon layer, with the first carbon layer located between the core and the second carbon layer. The first carbon layer comprises amorphous carbon and graphite. The second carbon layer comprises amorphous carbon and magnesium oxide particles. The amorphous carbon in the first carbon layer is formed by resin carbonization, and the amorphous carbon in the second carbon layer is formed by pitch carbonization. The particle size D90 of the nano-silicon material is 50 nm-150 nm. The flexible conductive polymer layer includes a conductive polymer having a conjugated structure; the conductive polymer is polyaniline or polypyrrole. The ratio of the mass of the conductive polymer to the total mass of the carbon layer and the core is (0.05-0.2):

1.

2. A method for preparing silicon-carbon material as described in claim 1, characterized in that, Includes the following steps: The nano-silicon material is coated with a carbon source to form a carbon layer on at least a portion of the surface of the nano-silicon material, thereby obtaining a first intermediate. The first intermediate is coated with a conductive polymer monomer to form a flexible conductive polymer layer on the surface of the first intermediate, thereby obtaining the silicon-carbon material.

3. The method for preparing silicon-carbon material according to claim 2, characterized in that, The process of coating the nano-silicon material with a carbon source includes: A first slurry containing the nano-silicon material and the first carbon source is subjected to a first drying process to obtain a first dried product. The first dried product is subjected to a first carbonization treatment to obtain a first intermediate. The first material, which contains the first intermediate and the second carbon source, is subjected to a second carbonization treatment to obtain the second intermediate; The second material, comprising the second intermediate, conductive polymer monomer, and oxidant, is reacted with an acidic solution, followed by a second drying process to obtain the silicon-carbon material.

4. The method for preparing silicon-carbon material according to claim 3, characterized in that, The first carbon source includes resin and graphite.

5. The method for preparing silicon-carbon material according to claim 4, characterized in that, The mass ratio of the nano-silicon material to the resin is 1:(0.1-0.3). And / or, the mass ratio of the nano-silicon material to the graphite is (1-3):

1.

6. The method for preparing silicon-carbon material according to claim 3, characterized in that, The first slurry also includes nitrogen-containing compounds; The nitrogen-containing compound includes at least one of melamine, urea, pyridine, pyrrole, ethylenediamine, trimethylamine, and aniline; The nitrogen-containing compound accounts for 1%-5% of the mass of the nano-silicon material.

7. The method for preparing silicon-carbon material according to claim 3, characterized in that, The first slurry further includes a dispersant, which includes at least one of hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and polyvinylpyrrolidone. And / or, the first dried product is subjected to isostatic pressing and shaping treatment, and then subjected to the first carbonization treatment; wherein, the pressure of the isostatic pressing and shaping treatment is 8000 N-20000 N; And / or, the temperature of the first carbonization treatment is 600℃-800℃, and the time is 2 h-4 h.

8. The method for preparing silicon-carbon material according to claim 3, characterized in that, The first material also includes a pre-magnesium agent, which includes at least one of magnesium hydroxide, dibutylmagnesium, and diethylmagnesium; The pre-magnesium agent accounts for 2%-6% of the mass of the first intermediate.

9. The method for preparing silicon-carbon material according to claim 3, characterized in that, The second carbon source includes asphalt, and the mass ratio of the asphalt to the first intermediate is (0.2-0.4):1; And / or, the temperature of the second carbonization treatment is 1200℃-1400℃, and the time is 3 h-6 h.

10. The method for preparing silicon-carbon material according to claim 3, characterized in that, The oxidant includes hydrogen peroxide and / or ammonium persulfate; And / or, the acidic solution includes a dodecylbenzenesulfonic acid solution and / or a hydrochloric acid solution; And / or, the reaction time between the second material and the acidic solution is 2 h to 10 h.

11. A negative electrode sheet, characterized in that, The silicon-carbon material prepared by the method for preparing silicon-carbon material as described in any one of claims 2-10 includes silicon-carbon materials.

12. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 11.

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